On dit,(Ne t’inquiètes pas ). ne + pronom personnel(tu) + verbe (s’inquiéter)+pas de la négation.

You should use "ne t'inquiète pas" (take note of the change in accent on the "e"). The reflexive verb is s'inquiéter.

"Ne t'inquiète pas" is the good sentence. If you want to speak like young people (i mean fast), but it is only for speak, you can say only : "T'inquiète pas"